Tubular woven fabrics may be utilized for prostheses implantable in soft-tissue to replace or repair damaged or diseased vessels or passages in the body. A general discussion of different types of woven fabric prostheses is set forth in U.S. Pat. No. 5,800,514, issued Sep. 1, 1998, the disclosure of which is hereby incorporated herein by reference.
Applications for implantable prostheses include, but are not limited to, applications in the vascular system, urinary tract, gastrointestinal tract, endocrine system, and lymphatic system. In particular, endoprostheses are used in the vascular system to prevent blood flow from rupturing a weakened section of a vessel. Such endoluminal conduits are generally affixed in a specified location in a vessel by means of stents, hooks, and/or other mechanisms which serve to secure the device in place. Endoluminal tubular devices or conduits can also be used in other vessels and passages in the body, such as in the esophagus and colon.
Vascular grafts have been used successfully for many years to replace segments of a diseased vessel by open surgical methods. These techniques, however, require long and expensive procedures, which have a high degree of risk associated with them due to the complexity of the surgical procedures and risks of surgery in general. Presently, less invasive techniques for treating abnormal, diseased, and traumatized vessels have become more prominent because they present less risk to the patient and are less complex than open surgery. As an example of such a procedure, a physician will make an incision in the femoral artery and introduce an endoluminal device by means of a catheter delivery system to the precise location of the damaged or diseased vessel. The device generally includes a stent and graft combination, which is deployed from the delivery system and affixed in place usually by use of a balloon catheter. The balloon catheter is used to expand the stents which are attached to, and most often contained within, the graft portion. Expansion of the stent serves both to anchor the graft and to maintain the graft and the vessel lumen in an open state. In some cases, self-expanding stents or the like are used. Stents made from shape-memory materials, such as nitinol, are also employed, whereby radial expansion or contraction of the stent is designed to occur at specified temperatures.
Effective use of tubular endoluminal prostheses, however, requires a high degree of precision in the diameter of the tube, such that the outside diameter of the prosthesis matches the inside diameter of the body lumen very closely, thereby conforming the prosthesis to the internal surface of the vessel. Vessels and lumens in the body, however, often vary in diameter and shape from one point or segment to another. In addition, vessels sometimes define a tortuous path between two points along their length. This is particularly true with vessels in the vascular system. Thus, tubular endoprostheses which are generally singular in configuration cannot accurately conform to all portions of a vessel lumen which have such variations present. In an attempt to conform to a varying diameter and/or angled or ill-shaped vessel, a prosthesis wall will often require bunching, or gathering, within the lumen of the vessel. Bunching of a prosthesis wall into an unsmooth configuration generally creates a more turbulent environment for blood flow and presents an increased and long-term potential for thrombosis.
More recently, in recognition of certain problems in delivering and implanting endoluminal prostheses, a thinly woven graft was made, which is designed to closely fit the inner lumen of vessels. However, these grafts have been made in single lengths or bifurcated structures using traditional weaving techniques, which have specific limitations as to the final shape of the product. Also, in conventional weaving techniques, the transition from one diameter to another occurs at a single point in the weave, creating a sudden change in the weaving pattern of the fabric in bifurcated or multi-diameter grafts. Such sudden changes create voids and gaps in a prosthesis wall and are considered undesirable.
Conventional weaving processes are commonly employed to fabricate various tubular-shaped products. For example, implantable tubular prostheses which serve as conduits, such as vascular grafts, esophageal grafts, and the like, are commonly manufactured using tubular weaving techniques, wherein the tubular product is woven as a flat tube. In such weaving processes, yarns are interwoven in different directions to create the tubular fabric. For example, a set of warp yarns run lengthwise parallel to the selvages, or edge portions, and represent the width of the product being woven. Fill yarns run from selvage to selvage at right angles to the warp and are interlaced between the warp yarns. The fill yarn is woven along the length of the warp yarns, with each successive pass of the fill yarn across the warp yarns for each side of the tube representing one machine pick. Weaving one fill yarn along the entire circumference of the tube, i.e., one filling pick, requires two picks of the weaving machine. Thus, two machine picks represent one filling pick in a tubular woven structure. As such, in a conventional woven product, the fill yarn is woven along the length of the warp yarns for a multiple number of machine picks. The resulting woven product is defined in length by the number of filling picks of the fill yarn and defined in width by the number of warp yarns in which the fill yarn is woven between.
Conventional techniques of forming tubular shapes have required manual cutting and suturing of standard woven tubular prostheses to the desired size and shape. Woven tubular prostheses, such as vascular grafts, having tapered diameter sections or tailored shapes are typically made by manual customization in the form of cutting, splicing, and/or tailoring with sutures.
Conventional grafts having more than one diameter are made by weaving separate grafts having different diameters and suturing the individual grafts together to make a continuous tube. The change in diameter between graft segments requires customized cutting to gradually transition from one diameter to another. For example, a surgeon may select a bifurcated graft having a 24 mm aortic section and equivalent 12 mm femoral sections for use in a patient. If one of the patient's femoral arteries is 10 mm in diameter, the surgeon would manually cut the appropriate femoral section and suture a seam along that section to form a leg more closely matching a 10 mm diameter. This customization requires cutting and suturing. Such customization relies heavily on the skill of the physician and allows little quality control in the final product. Customized grafts may not always be made in advance for a particular patient, since the requirements for such customization may not be known until the physician begins the procedure to introduce the device into the body. Additionally, suture seams take up considerable amounts of space when packed into a delivery capsule or other catheter-like device designed to deploy endoluminal prostheses.
Thus, conventional continuously woven bifurcated grafts suffer the disadvantages of gaps created at the bifurcation point between the prosthesis trunk and leg portions due to separation or splitting of the warp yarns, and featuring only leg portions having equal diameters. Different diameter leg portions could be accomplished only through customization. Such customization often requires manually cutting off one leg portion and suturing onto the trunk of another independently formed leg having a different diameter.
Complex shapes, such as tubular “S-shaped” or frustoconical-shaped woven sections have not been attempted using conventional weaving techniques due to the impractibility, intensive labor, and resulting high cost to the consumer. Indeed, such shaped tubes could not be woven practically using prior art techniques.
In addition to requiring manual cutting and sewing steps, manually customizing grafts often creates sutured seams that are disadvantageous in endoluminal prostheses, particularly because of the space that sutures occupy when tightly packed into a catheter delivery system. Furthermore, such seams disadvantageously contribute to irregularities in the surface of a graft, which may contact and possibly erode a weakened area of a vessel and/or increase the potential for thrombosis.
Recently, continuous flat-weaving techniques have been used to make graft diameter changes in a gradual manner, such that a tubular section transitions from one diameter to another diameter in a tapered fashion. U.S. Pat. No. 5,800,514 discloses a seamless tubular prosthesis and methods for producing seamless tubular prostheses. Techniques described in the patent permit the weaving of gradually-shaped tubular grafts in a continuous process to create seamless and void-free conduits for implantation in the body.
In general, U.S. Pat. No. 5,800,514 relates to flat-woven, implantable tubular prostheses, and in particular endoluminal grafts, which have been continuously woven to form seamless tubular products having gradual changes in diameter along their length. Such seamless grafts include tubular sections of various shapes formed from gradual changes in the number of warp yarns engaged or disengaged with the fill yarns during the weaving process. Changes in diameter and/or shape of a graft are accomplished by gradually engaging and/or disengaging selected warp yarns with the fill yarns in the weave pattern. Similarly, a bifurcation is achieved by disengaging selected warp yarns in the area of the intended split. The gradual transition can be accomplished using electronic jacquard looms controlled by computer software. Such engaging and/or disengaging of warp yarns can change the diameter of the tube or graft in a manner which creates a seamless and gradual transition from one diameter to another. Additionally, such engagement and/or disengagement can be used to create tubular vascular prostheses and the like which have any number of shapes.
Despite the potential advances achieved by such prostheses and techniques, such seamless prostheses have several disadvantages. In particular, the weaving techniques that are utilized to produce the prostheses and render them seamless, produce voids and gaps in the tubular wall.
Thus, there remains a need for developing tubular prostheses having smooth transitions from one diameter to another diameter that avoid gaps and voids in the tubular wall of the graft and provide an improved barrier against leakage in transition areas. There is a need for tubular prostheses having smooth transitions without voids and gaps at points of branching, such as in a bifurcated graft. There is also a need for tubular prostheses which allow for an increased rate of transition in tapered areas so as to provide more acutely angled transitions. There is also a need for tubular prostheses having smooth transitions that do not have excessive seams, such as with a seam sutured in the field. Further, there is also a need for tubular prostheses having smooth transitions that can be produced in various shapes in an efficient and economical manner.